The invention generally relates to electronic circuits, and more particularly to clock sensors.
Clock sensors are used to detect clock signals in many applications. Conventional clock sensors are configured with standard CMOS inverters. However, these CMOS inverters cannot detect signals with small swings and they draw a significant amount of power. Differential amplifiers having differential pair inputs are also used as clock sensors to detect small signals, but they also consume too much power. In a typical application, a clock sensor is used with a PLL (phase locked loop) in portable devices (e.g., laptop and handheld computers) for detecting incoming clock signals to xe2x80x9cwake upxe2x80x9d the circuits in the device to let the circuits be ready for operations. In these devices, low power consumption by clock sensors is especially important. These conventional clock sensors, however, typically consume a large amount of current and power while waiting for incoming clock signals, resulting in very inefficient use of power in the portable devices.
Therefore, there is a need for a clock sensor that requires low current and low power to operate on.
The invention provides a clock sensor that can be operated at very low current and power. This sensor can also detect an input clock signal with a very small amplitude to detect the presence of clock inputs.
According to one embodiment of the invention, a clock sensor comprises an input circuit configured to receive an input clock signal; a biasing circuit, connected to the input circuit, that is configured to receive the input clock signal and to provide biasing voltages; and a switching circuit, connected to the biasing circuit, that is configured to receive the biasing voltage and in response to the input clock signal, to provide a switching signal for switching an output circuit to generate an output clock signal.
According to another embodiment of the invention, the clock sensor further comprises an output circuit, connected to the biasing circuit, that is configured to receive the switching signal and to generate the output clock signal in response to the switching signal. In this embodiment, the input clock signal has a small amplitude and the output clock signal has a full amplitude.